Recently, the safety airbag system has found wider and wider application as a constraining device in vehicles to protect the heads of vehicle occupants during an accident such as a collision. All currently available safety airbags employ airbags that can be charged to form a soft air cushion, so as to buffer and absorb energy and hence reduce injuries to occupants. In case of a collision where it is necessary to activate a safety airbag, the airbag is charged with a large amount of gas generated by a gas generator and deployed in the form of a soft protection layer so as to buffer the collision impact onto the occupant's body. During the operation of the safety airbag, the gas generated by the gas generator quickly charges the airbag. It is an instantaneous expansion procedure, and hence the manner in which the airbag is deployed has significant influences on the airbag performance. The change of gas pressure and the final pressure value within the airbag also have significant influences on the degree of the protection that is provided to the occupant's body. In general, the conventional airbag is charged first, and is then deployed after being released. Since the charging speed is very quick, the great impact force generated in the forward direction when the airbag begins to expand will probably cause injury to the occupant's body; particularly in the case where the occupant's body is close to the airbag. In such circumstances, the great impact force can easily result in injury to the chest of an occupant who is very close to the airbag and moving against the expansion direction of the airbag. Furthermore, for the purpose of providing good protection, the volume of an airbag should not be too small. In general, the airbag at the driver's side is typically 30-60 L in volume, while the airbag at the passenger's side generally requires a volume of about 60-150 L. Thus, there are major requirements on the charging amount and the charging speed in order for air bags to be quickly and fully charged with gas and to be completely deployed in a short time.
Reference numbers in the drawings are as follows:
1—an upper air cushion
2—an air tube truss
3—a charging opening
4—a lower air cushion
5—an inlet opening
6—a discharging hole
7—a pulling belt
8—an upper fixing disc
9—a lower fixing disc
10—a tube pulling belt
11—a charging hole
21—a hollow air tube